This invention relates to wind and water turbines, and in particular to wind and water turbines having dual rotors.
Wind or water turbines are devices for converting wind or water power into electrical power and usually include a rotor, a gear box and a generator. In operation, wind causes the rotor to rotate and to provide a high torque, relatively low frequency input to the gear box. The gearbox transforms this input to provide a high, preferably constant, speed to the generator so that alternating current of the required frequency is produced.
In dual rotor turbines, combining the rotational energy from each rotor so that a single generator may be used has been achieved using bevel gears. It has also been achieved by connecting each turbine rotor to counter-rotating stator and rotor components of a generator, or having the first turbine rotor connected to first generator field rotor, and second turbine rotor connected to second field rotor. This arrangement means that the two rotors rotate in opposite directions and, for the first approach, the speed of the two rotors relative to each other cannot be adjusted.
One problem with existing wind/water turbine assemblies is the difficulty of maintaining a constant output speed to the generator. Another drawback is the relatively complex nature of wind/water turbine gearboxes, often utilizing multiple stage planetary gear systems.
US 2006/0093482 A1 discloses a windmill having counter-rotating screws. The screws are both located on the upwind side of an epicyclic gearbox, and serve to increase power supplied at a turbine location. The speed of the rotors can be controlled using a breaking mechanism, but the windmill is not configured to produce a constant output speed.